1. Field of the Invention
The present invention relates to a positive working photosensitive composition. In particular, the present invention relates to a positive working, aqueous base developable photosensitive polyimide precursor composition.
2. Description of the Related Art
Polyimide has been widely used in microelectronics as a protection layer, an insulation layer or a packaging material. Recently, photosensitive polyimide has attracted great interest not only because it can be easily synthesized but also because it is a substitute of the conventional photoresist in microelectronic applications.
Thus, various methods have been disclosed for preparing the positive-working photosensitive polyimide. U.S. Pat. No. 4,093,461 discloses a positive working photoresist composition comprising an orthoquinone diazide or naphthoquinone diazide and a polyamic acid condensation product. U.S. Pat. No. 5,399,655 discloses a positive working photodefinable polyimide precursor which makes use of chemical amplification based on photoacid catalyzed cleavage of acid labile poly (amic acetal esters). T. Ueno et al., Polymer Material Science Engineering., 77, 465(1997) describes a positive alkali developable photosensitive polyimide based on polyimide precursor with pendant carboxylic acid and DNQ (diazonaphthoquinone) sensitizer.
The positive working photosensitive composition of the present invention comprises a polyimide precursor, a photosensitive agent and a solvent. The polyimide precursor is a partially diazonaphthoquinone (DNQ) capped polyamic ester having the following structure: 
wherein, Ar1 is a tetravalent aromatic group and Ar2 is selected from the following groups: a tetravalent aromatic group, a aliphatic group, a heterocyclic group, or mixture of thereof. R is selected from following groups: an alkyl, an aryl, or other substituted aryl and n+m+x=1, wherein 0.05xe2x89xa6m+xxe2x89xa60.80, preferably 0.15xe2x89xa6m+xxe2x89xa60.75 and more preferably 0.25xe2x89xa6m+x less than 0.6; and Z is one of the following groups: 
The present invention also relates to the preparation of the positive working photosensitive polyimide precursor. In addition, the present invention teaches a photosensitive article comprising a support coated with a layer comprising a partially diazonaphthoquinone (DNQ) capped polyamic ester, a photosensitive agent and a solvent. Finally, the present invention teaches the process of using the positive working photosensitive composition to form the relief pattern.
In a preferred embodiment, the composition of the present invention comprises a partially diazonaphthoquinone (DNQ) capped polyimide precursor bearing phenolic hydroxyl groups, a photosensitive agent, and a solvent.
The polyimide precursor is made of a polyamic ester and the phenolic hydroxyl groups to render the aqueous base solubility of the polyimide precursor. The DNQ capping on the phenolic hydroxyl group can enlarge the difference of the dissolution rate before and after exposure and also can significantly reduce the dark film loss compared to the uncapped polyimide precursor. When the DNQ capping level increases to about 50% (in molar %), the dissolution rate of the exposed-film also increases. When the capping level increases to more than 50% (in molar %), the dissolution rate decreases abruptly.
The xe2x80x9cswellingxe2x80x9d phenomena also found in the un-dissolved portion of the film might be caused by the crosslink between the DNQ moieties and the polymer molecules when the capping level reaches to a level above 75% (in molar %). T Omote et. al., Macromolecules, 1990, 23, 4796-4802 discloses the same situation in their 100% DNQ capped polyimide system. In addition, the 100% DNQ capped polyimide precursor also shows poor adhesion to the silicon wafer.
A diazonaphthoquinone (DNQ) photosensitive agent is also added as the dissolution inhibitor for the uncapped portion of the polymer during the aqueous base development. After exposure to the actinic light such as x-rays, electron beam rays, ultraviolet (UV) rays and visible light rays, both the DNQ portions in the capped polyimide precursor and the added photosensitive agent are converted to the indenecarboxylic acid that increases the dissolution rate of the polyamic ester in the exposed region. Optionally, an adhesion promoter such as aminosilane may also be added to increase the adhesion.
After the photolithographic process, the patterned layer is converted to a heat resistant polyimide coating by application of additional heating. This resin composition can be used in microelectronic device fabrication applications as a thermal or mechanical stress buffer coating, an alpha particle barrier film, an interlayer dielectric, or a packaging material.
The present invention provides a positive working photosensitive composition comprising a partially DNQ capped polyamic ester bearing hydroxyl groups, having the following structure: 
wherein Ar1 is a tetravalent aromatic group having one of the following structures but is not limited to moieties with the structure: 
wherein X1 is 
wherein Zxe2x95x90H or alkyl, y=1xcx9c20 and Ar2 is a tetravalent aromatic group having one of the following structures: 
In addition, Ar2 may be an aliphatic group, a heterocyclic group, or mixtures thereof. R is an alkyl, aryl, or other substituted aryl having one of the following structures but is not limited to moieties with the structure: 
wherein n+m+x=1 and 0.05xe2x89xa6m+xxe2x89xa60.80, preferably 0.15xe2x89xa6m+xxe2x89xa60.75 and more preferably 0.25xe2x89xa6m+xxe2x89xa60.6; and Z is one of the following groups: 
The photosensitive agent consists of a diazoquinone compound and is about 1-50% weight percentage of the composition. The suitable diazoquinone compound is one of the following structures: 
wherein D is H or one of the following compounds: 
The positive-working photosensitive composition is used as a solution dissolved in a solvent. Suitable solvents include, but are not limited to, organic solvents, such as N-methylpyrrolidone (NMP), xcex3-butyrolactone (GBL), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide(DMF), or mixtures therefore. Optionally, an adhesion promoter such as the aminosilane may be further added to increase the adhesion of this composition.
The present invention also teaches a process for forming a relief pattern comprising the steps of: (a) coating the positive-working photosensitive composition solution on a suitable substrate by a method such as spin coating; (b) prebaking the coated substrate; (c) exposing the prebaked coated substrate to the actinic light; (d) developing the exposed coated substrate with an aqueous base developer, thereby forming a developed substrate; and (e) curing the developed substrate, thereby forming a relief pattern.
In the first step, the positive working photosensitive composition is coated on a suitable substrate such as a silicon substrate and then a photosensitive article comprising a support coated thereon a layer of positive working photosensitive composition is formed. The coating methods include but are not limited to spin coating, roller coating, screen coating, curtain coating, dip coating, and spray coating. In a preferred embodiment the resulting film is prebaked at a temperature of 7014 120xc2x0 C. for several minutes to evaporate the solvent. Subsequently, the coated substrate is exposed to the actinic light through a mask. X-rays, electron beam rays, ultraviolet rays, visible light rays and the like can be used as the actinic light sources.
The exposed coated substrate is then developed by an aqueous base developer and a relief pattern is obtained. The aqueous base developer includes the solution of alkalis such as an inorganic alkali (e.g., potassium hydroxide, sodium hydroxide), primary amines (e.g., ethylamine), secondary amines (e.g., diethylamine), tertiary amines (e.g. triethylamine), quaternary (e.g., tetramethylammonium hydroxide), and mixture thereof. The preferable developers are those containing tetramethylammonium hydroxide. The development can be carried out by means of immersion, spray, pudding or other similar methods.
The relief pattern is then rinsed by deionized water. In a perferred embodiment the film is then cured at 250-400xc2x0 C. to convert the polyamic ester precursor to the heat resistant polyimide.